1. Field of the Art
This invention relates to a piezo-electric device type actuator suitable for use on a wire dot printer or the like.
2. Description of the Prior Art
Recently, in step with the acceleration of the printing speed in wire dot printers, laminated piezo-electric devices are increasingly resorted to for driving printing wires on a printing head. The laminated piezo-electric devices usually contain a plural number of internal electrodes and a couple of external electrodes, which are connected to the internal electrodes, and are required to have high reliability since they are driven under high voltage and severe operating conditions.
Referring to FIG. 1, there is illustrated a conventional printing element using a laminated piezo-electric device. The printing element 1 is constituted by a displacement magnifying mechanism 2, an actuator 3, a base member 4 linking the displacement magnifying mechanism 2 and the actuator 3, and a movable block 5. The displacement magnifying mechanism 2 is constituted by an armature 6, and a pair of leaf springs 7 and 8 which are disposed in parallel relation with each other to support one end of the armature 6. The leaf spring 7 is fixedly secured to the base member 4, while the other leaf spring 8 is fixedly secured to the movable block 5. A printing wire 9 is securely fixed to the other end of the armature 6.
As best shown in the perspective view of FIG. 2, the actuator 3 is constituted by a laminated piezo-electric device 10, blocks 11 and 12 which are located at the opposite ends of the laminated piezo-electric device 10 in such a manner as to sandwich the latter, and resilient plates 13a and 13b which are extended along the opposite sides of the laminated piezo-electric device 10 and welded to the latter by laser welding at the positions of points P while applying a predetermined compressive force to the laminated piezo-electric device 10.
The blocks 11 and 12 are fixedly bonded to the movable block 5 and base member 4, respectively, by the use of an adhesive. The block 11 is linked to the base member 4 through a leaf spring 15 for the purpose of stabilizing the operation of the laminated piezo-electric device 10.
The laminated piezo-electric device 10 is constituted by a plural number of laminated piezo-electric ceramics layers, a plural number of internal electrodes which are sandwiched between the respective piezo-electric ceramics layers, a couple of external electrodes which are alternately connected to every other internal electrode, and lead wires 14a and 14b which are connected to the external electrodes 13a and 13b, respectively.
Upon applying a drive voltage to the lead wires 14a and 14b, the laminated type piezo-electric device 10 is deformed to stretch by ten and several micrometers. As a result, the movable block 5 is pushed in the leftward direction in FIG. 1, and the armature 6 is turned about its lower end portion by bi-metal action of the leaf springs 7 and 8 to magnify the displacement of the movable block 5, thereby driving the printing wire 9 to protrude forward by several hundred micrometers. As a result, the wire 9 is hit against the platen, through an ink ribbon and a printing paper sheet which are not shown, to print a dot on the paper.
However, when the actuator of the above-described construction in which the blocks 11 and 12 at the opposite ends of the laminated type piezo-electric device 10 ar bonded to the movable block 5 and base member 4 by means of an adhesive, there has been a problem that, due to insufficient strength in the bondage of the adhesive, the blocks are apt to be loosened or detached in the course of printing operations, thereby failing to operate in a stable state in terms of performance quality. Damage is especially likely to occur on the part of the movable block which is subjected to bending stress in addition to tensile stress.